This description relates to a coil-driving apparatus of electronic magnetic contactor, and more particularly to a coil-driving apparatus of electronic magnetic contactor changing circuit units in an existing analog scheme into those in a digital scheme by means of a PWM (Pulse Width Modulation) controller of low power consumption to reduce the number of analog components and to minimize power consumption.
Generally, an electronic magnetic contactor, which is an apparatus connected to an electrical connection path to supply or block power to a load in a system such as a building, a factory, and a ship, etc., prevents the load from being burnt out.
The electronic magnetic contactor, which is equipment for opening and closing a contact point by using an electromagnetic principle, allows the contact point to be contacted when a current flows and allows the contact point to be separated when a current does not flow, by applying a constant voltage to a coil.
FIG. 1 is a block view showing a constitution of a coil-driving apparatus of a general electronic magnetic contactor.
Referring to FIG. 1, the coil-driving apparatus of the general electronic magnetic contactor includes an input filter unit 102, a rectifying unit 104, an input voltage detecting unit 106, a constant voltage unit 108, an operation control unit 110, an overvoltage prevention unit, a temperature compensating unit 120, a control voltage level controlling unit 122, a sawtooth generation unit 124, a PWM output unit 126, a switching unit 260, and a surge absorbing unit 280.
The input filter unit 102 absorbs a surge voltage to remove noise from a voltage inputted from an input terminal 100.
The rectifying unit 104 rectifies a voltage outputted from the input filter unit 102 to output a direct current power.
The input voltage detecting unit 106 detects a voltage level of the direct current power outputted from the rectifying unit 104.
The constant voltage unit 108 receives the direct current power outputted from the rectifying unit 104 to output a constant voltage. The rectifying unit 108 supplies a driving power for driving respective units.
The operation control unit 110 compares the voltage level detected by the input voltage detecting unit 106 with a pre-set reference voltage level and then outputs control signals according to the comparative results thereof. It is preferable that the pre-set reference voltage be generated through the constant voltage unit 108.
More specifically, the operation control unit 110 includes a comparing/judging unit 111 and a time determining unit 112, wherein the comparing/judging unit 111 compares the voltage level detected by the input voltage detecting unit 106 with the pre-set reference voltage level to output suction signals, when the voltage level of the input voltage detecting unit 106 is larger than the reference voltage level, and to output release signals when the voltage level of the input voltage detecting unit 106 is smaller than the reference voltage level. In other words, if the control signals outputted from the comparing/judging unit 110 are suction signals, the operation control unit 110 performs a suction operation, and if the control signals outputted from the comparing/judging unit 110 are release signals, the operation control unit 110 performs a release operation. When the comparing/judging unit 111 outputs the suction signals, the time determining unit 112 determines a maintenance time of the suction signals to transfer it to a control voltage level controlling unit 122. The reason is that since a large amount of current is generally needed at an early stage for contacting the contact point of the electronic magnetic contactor, the suction signals are continuously maintained for the pre-set time to provide the current so that the contact point can contact each other. Also, the time determining unit 112 transfers the release signals outputted from the comparing/judging unit 111 to the control voltage level controlling unit 122.
The overvoltage prevention unit and the temperature compensating unit 120 are configured of an overvoltage prevention unit and a temperature compensating unit. The overvoltage prevention unit controls the control voltage level controlling unit 122 not to generate signals having a predetermined level, when the voltage detected by the input voltage detecting unit 106 is larger than the pre-set voltage. The temperature compensating unit, which is configured of a sensor or a circuit measuring a peripheral temperature, generates control signals in order that the levels of the signals generated by the control voltage level controlling unit 122 depending on temperature change can be controlled.
The control voltage level controlling unit 122 generates signals having a predetermined level in order that a pulse width of PWM signals outputted from a PWM output unit 126 in response to the control signals inputted from the time determining unit 112 of the operation control unit 110 can be controlled.
The control voltage level controlling unit 112 neither controls the level of the signals nor outputs the signals by receiving the control signals of the overvoltage prevention unit and the temperature compensating unit 120.
The sawtooth generation unit 124 outputs sawtooth signals for a predetermined period as the control voltage level controlling unit 122 outputs the signals of a predetermined level.
The PWM (Pulse Width Modulation) output unit 126 compares the signals generated by the control voltage level controlling unit 122 with those outputted by the sawtooth generation unit 124, and then outputs PWM signals according to the comparative results thereof.
The switching unit 128 allows current flowing on a coil 130 to be conducted or to be blocked by being switched according to the PWM signals generated from the PWM output unit 126. In other words, the switching unit 128 is switched according to the PWM signals so that current flowing on the coil 130 can be controlled.
The surge absorbing unit 280 absorbs counter electromotive force generated from the coil 130.
In the general electronic magnetic contactor described above, many units are included for controlling the coil. In particular, main units for generating the PWM signals, such as the overvoltage prevention unit, the temperature compensating unit 120, the control voltage level controlling unit 122, the sawtooth generation unit 124, and the PWM output unit 126 are in an analog scheme whereby the analog components constituting the respective units becomes numerous to cause various problems.
First, circuits become complicated due to the components of the respective units, and a circuit board becomes large for inserting the components into the circuit substrate to that extent.
Also, errors occur due to use of the analog components and defect generation rate increases due to multiple analog components.
Also, current consumed in the circuit becomes large to generate much heat thereby the components are deteriorated or burnt.
Finally, there have been attempted to solve the above problems by using components having a small error range for the components constituting the respective units, such as the overvoltage prevention unit, the temperature compensating unit 120, the control voltage level controlling unit 122, the sawtooth generation unit 124, and the PWM output unit 126. However, these problems have not been easily solved due to expenses, power consumption and other reasons.